Some people like to engage in walking or jogging as a form of exercise after dark or before dawn, thereby making themselves vulnerable to a traffic accident or death. It is therefore suggested that such exercisers as mentioned above should wear a pair of shoes having a reflector or a fluorescent device attached thereto as a means of warning the drivers. However, the reflector is generally effective only at the time when the beams of light coming from a motor vehicle are projected on the reflector appropriately. The effect of the fluorescent device is generally poor after dark or before dawn, because the fluorescent device is most effective in a place where it is very dark.